I am trying to understand the content-biasing. Somehow it has no effect on our installation.

Stepping through the code learns me that the query-string did change: the modified boost values like &bq=type:audio^1.0 show up, but have no effect on the search-results' sort-ordering or the $result["score"] value. the score remains exactly the same, no matter how high or low a bias is set.

Could it be cached somewhere on the solr server? (clear cache has no effect, code does not hint at caching it). Is this a known bug? Or an issue with the schema.xml?